The present invention relates to an active microwave reflector with electronic scanning, capable of being illuminated by a microwave source in order to form an antenna.
It is known to produce antennas comprising an active microwave reflector. The latter, also called a xe2x80x9creflect arrayxe2x80x9d, is an array of phase shifters which can be controlled electronically. This array lies in a plane and comprises an array of elements with phase control, or a phased array, placed in front of the reflecting means, consisting, for example, of a metal ground plane forming a ground plane. The reflect array especially comprises elementary cells each one producing reflection and a phase shift, variable by electronic control, of the microwave that it receives. An antenna of this sort provides considerable beam agility. A primary source, for example a horn, placed in front of the reflect array emits microwaves toward the latter.
The phase shifts applied by the elementary cells vary discretely. Since the phase shifts are equally distributed, they are controlled digitally according to a number of bits. If this number is called N, the phase-shift step is then 2xcfx80/2N. The accuracy of a phase shift is therefore equal at best to one phase-shift step. The lack of accuracy leads to certain drawbacks, in particular it leads to the existence of relatively high secondary lobes and poor positioning accuracy of the antenna.
One aim of the invention is especially to alleviate the aforementioned drawbacks. To this end, the object of the invention is an active microwave reflector, capable of receiving an electromagnetic wave which is linearly polarized in a first given direction Oy. The reflector according to the invention comprises a set of elementary cells placed side by side over a surface, each cell comprising a phase-shift microwave circuit and a conducting plane placed substantially parallel to the microwave circuit, the phase-shift circuit comprising at least two half-phase shifters. A half-phase shifter comprises at least one dielectric support, at least two electrically conducting wires, substantially parallel to the given direction Oy, placed on the support and each one bearing at least one semiconducting element with two states, each wire being connected to conductors controlling the semiconducting elements, these conductors being substantially normal to the wires, and two conducting zones placed toward the periphery of the cell, substantially parallel to the control conductors. There are at least three control conductors in each half-phase shifter which are electrically insulated from one half-phase shifter to the other in order to control the state of all the semiconducting elements independently of each other. The geometrical and electrical properties of the half-phase shifters are such that a given phase-shift value (dxcfx861, . . . dxcfx868) of the electromagnetic wave which is reflected by the cell corresponds to each of the states of the semiconducting elements. The reflector furthermore comprising an electronic circuit (36) for controlling the state of the semiconducting elements.
The invention also relates to an antenna fitted with such a reflector.
The main advantages of the invention is that it enables a low bulk and low weight reflector to be produced, that it is suitable for many types of antennas, that it improves heat exchange between the reflector circuits and the outside, that it provides great reliability and that it is economical.